Our studies have been oriented to define the role of Ig classes in the immune response/pathophysiology in viral diseases. The immune complexes of Aleutian diseases (AD) mink are being analyzed to explain the predominant deposition of IgA in glomerulae of terminal AD mink. Also, the aberrant lymphoproliferation in AD mink is being studied by analyzing T cell mitogen responses to protein and AD virus antigens, SV-40 inoculated into Syrian hamsters has been found to induce B cell lymphomas which are preferentially of an IgG class. Some of these tumors also secrete IgG which is monoclonal and the product varies from whole Ig molecules with free L chains to primarily free H chains. In contrast, IgM synthesis was preferentially enhanced by injection of Freund's adjuvant combinations into Syrian hamsters. The essential mycobacterial component of Freund's adjuvant is present in the cell wall but is not MDP.